This invention relates generally to lock systems for steering columns and more particularly to those which selectively lock the column against tilt or rake and telescoping movements in the event of a collision.
Land vehicles manufactured today are frequently equipped with convenience features as well as safety features. The convenience features include steering columns with tilt adjustments, rake adjustments and telescope adjustments. These adjustments can be stepped adjustments or infinitely variable adjustments. The safety features include air bags and energy absorption devices. An air bag for a vehicle driver is generally mounted in the steering wheel. Energy absorption devices for drivers include mechanisms that permit a controlled collapse of the steering column.
Steering wheel mounted air bags are designed to deploy in the event of a collision to provide protection to the driver. It is desirable that the column remain fixed in the position of adjustment selected by the driver throughout the event of the collision to afford maximum performance and protection offered by the air bag. In addition to the airbag, adjustable position columns are typically fitted with energy absorption (xe2x80x9cEAxe2x80x9d) systems, which may take the form of deformable energy absorbing straps or the like, that allow the column to collapse during a collision at a controlled rate when impacted by the driver to offer added protection to the driver. It is best that the column remain locked in the adjusted position and not slip to afford maximum performance of the EA system.
Steering columns with infinitely variable rake and telescope adjustments rely upon friction to maintain selected positions of adjustment. During normal operation and in a typical collision, the friction is generally sufficient to hold the adjustment systems against slippage. However, the frictional locking system does not provide a positive mechanical lock that would preclude movement of the adjustment parts under extreme conditions where the impact force on the column may be very high.
A locking system for an adjustable steering column according to the invention comprises at least one toothed rack and at least one associated toothed locking device movable selectively into engagement with the toothed rack. The locking device is normally supported out of engagement with the toothed rack to permit usual adjustment of the column, but is movable into meshing tooth-to-tooth locking engagement with the teeth of the rack in response to an applied impact force on the column by the driver during a collision event to positively lock the column against inadvertent adjustment during controlled collapse of the column. According to a further aspect of the invention, the locking system is for a column having rake and telescoping adjustment features and includes a rack associated with the relatively movable telescoping adjustment components of the column and a rack associated with the relatively movable rake adjustment components of the column. Also included is a toothed locking device associated with the racks which is selectively movable into positive locking engagement in response to the applied impact load on the column to preclude both rake and telescoping movements of the column during the controlled collapse of the column in a collision event.
According to still a further aspect of the invention, the racks associated with the relatively movable rake and telescoping components are arranged adjacent one another and the locking device comprises a common locking element having teeth engageable with the teeth of both the rake and telescoping racks so as to simultaneously prevent both rake and telescoping movements when engaged.
According to still a further aspect of the invention, the set of rack teeth of the rake and telescoping racks are disposed at an acute angle and the teeth of the common locking element are likewise set at an acute angle such that the locking element is forced into wedged locking engagement with the racks to enhance the locking power of the locking system.
According to a preferred embodiment of the invention, the steering column includes a jacket assembly having a lower jacket and an upper jacket that telescopically receives the lower jacket. A telescopic steering shaft is journaled in the jacket assembly. A rake support on the lower end of the lower jacket pivotally supports the vehicle steering column for pivotal movement about a transverse horizontal rake axis. A compression bracket fixed to the upper jacket has at least one telescope slot. At least one rake bracket, for supporting the compression bracket has a rake slot. A rake bolt passes through the rake slot and the at least one telescope slot and is tightened to frictionally hold a rake position and a telescope position. A rake tooth rack in the rake slot faces away from the rake axis and extends upward and rearwardly away from the rake axis. A telescope tooth rack in the at least one telescope slot is substantially parallel to the steering shaft and faces upwardly. A wedge lock on the rake bolt has a plurality of telescope teeth engageable with the telescope tooth rack and has a plurality of rake teeth engageable with the rake tooth rack. A connection between the rake bolt and the wedge lock permits the wedge lock telescope teeth to move into engagement with the telescope tooth rack in response to rotation of the rake bolt in a direction that tightens the rake bolt.